Stainless Steel - 400 series stainless steel ferritic heat resistant characteristics
General introduction and application
409HP 409 (UNS S40900) steel is resistant ferritic. Stainless steel for automotive exhaust components to ensure a good resistance to oxidation and corrosion . 1961 developed this alloy is used as a car muffler , and since then this versatile stainless steel is used for piping manifold automobile tubes, exhaust pipes, catalytic converters , mufflers and tailpipes . 409 steel outstanding formability , weldability and corrosion resistance has been so widely used in many other places, such as culverts , home furnaces , automotive thermostats, fuel filter adapter housing and farm equipment. 409 (UNS S40900)
Ferritic stainless steel for use in the most favorable , but in HAZ some industrial applications will produce intergranular corrosion. The content of the alloy Ti and Nb ratio very carefully , resistant to corrosion between the sensitivity and possible grain HAZ or parent metal heat occurring in other circumstances . Titanium nitride is another less surface defects characteristic of the alloy. Stabilizing element can achieve the best balance ratio weldability and is not annealed after welding to restore ductility . The formability and toughness are increased. 409HP (USN S40930) alloy is a patented stainless steel chemical composition. Like other 409 alloy , 11% Cr content so greatly enhanced corrosion resistance than steel . The alloy has sufficient resistance to oxidation and corrosion resistance , is an excellent choice for automotive exhaust system applications. The hot end of the discharge may take an amount of 18% Cr alloy . 409HP alloy good processability , but also conducive to the application in the outside of the car.
Chemical composition
Mechanical properties:
409HP alloy is in the normal processing temperature of the ferrite single phase microstructure , wherein the deposition of the scattering carbonitride of Ti and Nb . The ratio of its chemical composition is very careful to avoid the annealing temperature or in the weld heat affected zone along with the formation of austenite and martensite formation . Many long- ferrite placed 700-1100 ℉ (370-590 ℃) temperature range after embrittlement . At a temperature of about 885 ℉ (475 ℃) when this embrittlement fastest, often called "885 ℉ (475 ℃) embrittlement ." This is called the α ' martensite Cr -rich deposition of the second phase . 885 ℉ (475 ℃) embrittlement rate to a great extent depends on the Cr content of the alloy . Cr content is less than 12% , rarely 885 ℉ (475 ℃) embrittlement.
Stress rupture
409 and 439 alloys similar fracture data in 1200 ℉ (649 ℃) , the anti- fracture time and 439 alloys under special stress a little bit longer . 439 and because the higher the Cr content , in 1500 ℉ (816 ℃) under the stress of 1500psi (10.3 MPa) or less, the longer time of its resistance to fracture .
Fatigue
Bending fatigue tests with 409 annealed alloy showed fatigue after 10 million cycles ( lasting ) limit of 30,000-34,000 psi. This and other shows that ferritic stainless endurance limit is typically 50-55 % of its tensile strength data is consistent.
Toughness
Like stainless steel , under the impact load, will undergo transition from ductile to brittle when the temperature drops. " Ductile - brittle transition temperature " (DBTT) is a function of many factors , including the heat treatment, micro- structure, stress loading rate notch sharpness , thickness and homogeneity of the material . Typically , the thickness of 3/16 "(4.77mm) stainless steel plate 409 and above , the DBTT is higher than room temperature , i.e., 150-250 ℉ (66-121 ℃), indicates that the sheet may be difficult due to the occurrence of brittle fracture process . 409HP sheet [ 3/16 "(4.77mm) ] showed very close to or below room temperature DBTT values. 0.079 "(2 mm) of 409HP alloy, which are longitudinal and transverse DBTT of -50 ℉ (-46 ℃). Typically much lower than this value , and the processing temperature, is showed ductile mode machining . More predictable a thin sheet or strip has a DBTT lower value .
Corrosion resistance
Cr content in the alloy 409 was 11% , compared with steel , the corrosion resistance considerably increased. However, the content of Cr and other , particularly at the higher levels of the high Mo steel compared to its corrosion resistance is relatively low. Nevertheless, many of the alloy in the automotive and non-automotive applications can provide adequate resistance to corrosion and oxidation resistance . Atmosphere (Atmospheric) in the atmosphere than carbon steel corrosion resistance . Chloride (chlorides) compared with other ferritic stainless steel in chloride-containing environments , 409 alloy has excellent performance of anti- stress corrosion cracking . Generally speaking in the presence of chlorides at capacity 409 alloy resistance to pitting and crevice corrosion is minimal. 409 alloy susceptible to pitting , that even at low chloride water may be relatively low value of its fragmentation . Higher Cr content alloys, such as 439 or 304 ferritic steels austenitic steel , they are 18% Cr content , their resistance to pitting and crevice corrosion performance is much better , which is the fragmentation of the possible values higher . Contains high Cr and Mo containing 444 alloy (18Cr-2Mo), in the presence of chlorides at the resistance to pitting and crevice corrosion higher.
Intergranular corrosion
409 standard chemical composition of the alloy weld heat affected zone can not be avoided or undergo certain heat -sensitive parent metal. Industry reports show 409 automotive welding alloys occurred on non-automotive exhaust system components and the manufacture of heat exchangers such as welded pipe field failures , even if it meets the requirements of ASTM on stabilization , at least Ti = 6 × C. Cause of the failure is intergranular corrosion of the heat affected zone . 409HP alloy Ti and Nb are stable , greatly improving the anti- sensitivity ( chromium carbide precipitation ) and possible resistance to intergranular corrosion . Stability allows the use of double low Ti -containing material to the surface of the Ti -related defects to a minimum. Adding Ti and Nb to ensure the Nb carbonitride as a precipitate of N and C , thereby preventing sensitivity and may cause precipitation of inter- crystalline corrosion chromium carbonitride . 36 409 alloy furnace used to study the stability requirements . Each furnace contains enough to satisfy Ti steel ASTM 409 standard stability requirements , i.e., Ti ≥ 6 × C. In addition to Ti, furnace 11 further comprising a stabilizing element Nb. Unlike other ferritic stainless steel body , there is no standard ASTM method to detect Cr content of 11% and sensitivity of depleted ferritic alloys of Cr . ASTM A763 does have a test on the Cr content of the alloy , but the requirements are too strict , not for 409 alloy .
Oxidation resistance
Data show that about 1400 ° F (760 ° C), Cr content of 11% AL409HP has excellent oxidation resistance. At higher temperatures it is not satisfactory from the high loss rates and scales material.
Fabrication
409HP alloy easy to adopt and apply to other low carbon stainless common standard method forming, machining and welding. Can be shaped molding method and moldability (Formability) 409HP very low carbon steel alloys with the same . 409HP alloy ( and other 409 variants ) and carbon material is ferrite , which has a body centered cubic crystal structure. These materials may be molded metallurgical factors are very similar. For example , as measured for hardened stretch formability and strain hardening index value "n" , the annealed alloy 409HP falls within the range 0.22-0.25 , which is also typical of low carbon steel , stretch formability indicate 409HP similar to the low void of carbon steel. Drawability 409HP alloy and carbon steel for deep drawing is also similar . The average strip ratio of the strain it falls within the range of 1.2-1.6 , indicating a good deep drawing properties with similar deep drawing quality steel . Since 409HP sheet DBTT may be greater than room temperature , it is necessary to strictly forming, bending or stamping before heating to 300-500 ° F. Forming radius and fully remove the burr trimming is also conducive to forming. (UNSS40900) and 409 HPTM (UNSS40930) steel strip FLD 409 alloys have been found to have a wide range of applications in the processing of vehicle emissions systems. Such as low carbon steel plate products for routine bending, shearing , cutting, stamping and punching. Part by drawing or deep drawing is quite complex shapes. 409HP conventional alloy pipe bending , steel pipe flanges in accordance with the processing methods , expanding or reducing . Now able to adopt hydroforming method successfully 409HP alloy into a desired shape .
Machining
Machining performance 409HP steel alloy is closer than the 300 series austenitic stainless steel. 409HP recommended speed machining alloy B-112 steel grades , often used as a standard 60% cutting steel , 409HP micro structure, the alloy of titanium and niobium carbonitride hard particles will wear rate of the tool faster than the processing of steel .
Welding
Typically used for welding of carbon steel can be easily welded 409HP alloys, including high-frequency resistance welding , GTAW or TIG, GMAW or MIG, electron beam and laser welding techniques. Although commonly used self- penetration welding , pipe often used when 409Cb as welding filler metals . The chemical composition of the filler metal ratio 409Cb to be very careful to avoid the martensitic weld deposit , which the condensate drainage system in the car as the acidic environment, greater than 409HTM mother corrosion. Similarly, suitable metal 409HP filled with austenitic stainless and carbon steel or alloy itself and welded austenitic stainless steel . You can also consider using filler metal welding AL409HP Ni -based alloys because of their thermal expansion closer . GTMA GMA welding process and to use a common inert gas shield (Ar or He). Since 409HP (UNSS40930) alloy composition and the ratio of good chemical stability of Ti and Nb metal weld heat affected zone of the parent to maintain corrosion resistance and mechanical properties, welding no guarantee doping C and N. Take appropriate steps to avoid weld clean doping C, suitably with an inert gas ( such as Ar or He) shielding to avoid doping N.
Brazing
A standard 409 (UNSS40900) alloy compared , 409HP (UNSS40930) chemical composition has two distinct advantages in terms of solderability . First , Ti alloy having a low content 409HP would hinder the brazing titanium alloys to minimize the hydrophilic advantages. Second , Nb content 409HP (UNSS40930) combined with a low Ti content in the alloy having excellent stability , brazing cycle strong .
Availability (Availability) 409HP (UNSS40930) stainless steel products can shape sheet, strip and plate . You can also use this alloy tubing.