KR20090013769A - Low carbon alloy steel tube having ultra high strength and excellent toughness at low temperature and method of manufacturing the same - Google Patents

Abstract

A low carbon alloy steel tube and a method of manufacturing the same, especially for a stored gas inflator pressure vessel, in which the steel tube consists essentially of, by weight: about 0.06% to about 0.18% carbon, about 0.3% to about 1.5% manganese, about 0.05% to about 0.5% silicon, up to about 0.015% sulfur, up to about 0.025% phosphorous, and at least one of the following elements: up to about 0.30% vanadium, up to about 0.10% aluminum, up to about 0.06% niobium, up to about 1% chromium, up to about 0.70 % nickel, up to about 0.70 % molybdenum, up to about 0.35 % copper, up to about 0.15% residual elements, and the balance iron and incidental impurities. After a high heating rate of about 100 °C. per second; rapidly and fully quenching the steel tubing in a water-based quenching solution at a cooling rate of about 100 °C. per second. The steel has a tensile strength of at least about 145 ksi and as high as 220 ksi and exhibits ductile behavior at temperatures as low as-100 °C.

Description

LOW CARBON ALLOY STEEL TUBE HAVING ULTRA HIGH STRENGTH AND EXCELLENT TOUGHNESS AT LOW TEMPERATURE AND METHOD OF MANUFACTURING THE SAME}

This PCT application claims the benefit of US Provisional Application No. 11 / 395,322, filed April 3, 2006.

The present invention relates to a low alloy steel tube having ultra high strength and good rigidity at low temperatures, and also to a method for producing such a steel tube. The steel tube is particularly suitable for producing the components of a container for an automobile restraint system, which is for example an automobile airbag inflator.

In addition, optional steel compositions in low carbon, low alloy categories and various heat treatment processes have been developed and tested to reduce manufacturing costs.

Japanese Patent Publication No. 10-140249 [filed November 5, 1996] and Japanese Patent Publication No. 10-140283 [filed November 12, 1996] describe general steel chemistry known to be useful as automobile airbag inflators. These documents refer to the absence of heat treatment, stress relief, and normalizing or quenching and quenching as final conditions. No mechanical property is mentioned in the claims. Of the various examples, only Example 21 was quenched and quenched steel, but the reported UTS was only 686 MPa (99 ksi). Even the highest defined mechanical properties of Example 26 were relatively low, with a maximum UTS of 863 MPa (125 ksi). Thus, these publications relate to a relatively low rating (the intention is 590 MPa (86 ksi)). In addition, these publications show ductility at low temperatures with a stable load drop (DW) type test at -40 ° C. The currently accepted experiment to prove ductility at low temperatures is an explosion test, which is more effective at showing brittleness. Most of the examples shown in these documents that are presumed to be softened after the DW test, in fact did not exhibit ductile behavior at low temperatures in the burst test and, therefore, lack of compliance with governmental regulations (e.g. US DOT) to specific airbag inflators. It is believed that they are not qualified to apply.

Japanese Patent No. 2001-49343 [filed October 8, 1999] focuses only on steel for use in the manufacture of electro-resistant-welding tubes (ERW process). The claims specify the various aspects of the ERW process and any heat treatment for soaking or quenching and quenching, stretching in any subsequent cold working, and any subsequent heat treatment (soaking or quenching and quenching). This document only focuses on two differences, a very common steel chemistry, one with low carbon steel and the other without general limitations on several alloying elements. This document does not merely suggest the possibility of quench heat treatment. Several examples of quenching and quenching materials are provided, but the mechanical properties obtained are relatively low. The maximum result achieved is 852 MPa (123 ksi) in quench and quench test 18.

Steel “chemistry” is JP 10-140249, JP 10-140283, respectively; The chemistry, published by Sumitomo in JP 2001-49343 and subsequently published in US 6878219 B2 by Kondo et al., Or US 2005/0039826 A1, has actually been around since 1990. A broad range of steel is defined to include general purpose steel SAE 1010 manufactured and sold in the United States. Applicants know that the total of P is generally 0.025 or less and the S total is 0.01 or less, as described in the application mentioned for years SAE 1010 steel grades manufactured with modern technology.

Additional literature describing the prior art situation of steel for airbag applications includes its several published continuing applications, including US 6386583 B2 and US 2004/0074570 A1 and US 2005/0061404 A1 by Erik. do. These documents do not suggest any benefit as taught here from extremely rapid induction austenitization and subsequent ultra-fast water quenching, and only allow use of such rapid quenching and then no quenching steps. In addition, JP 10-140283 describes a chemistry that overlaps with US 6878219 B2, which has only a slightly lower maximum (0.02) for P and a slightly higher maximum (0.02) for S. Although patent application US 2002/0033591 Al has widely proposed the possibility of quenching without quenching, claims 6 and 7 do not mention the need for quenching to obtain the claimed mechanical properties, but these claims require at least two heat treatments. do.

Airbag inflators for vehicle occupant restraint systems require strict standards in construction and function. Therefore, stringent procedures and tolerances are imparted to the manufacturing process. Field experience indicates that this industry has been successfully adapted to past structural and functional standards, but improved and / or new properties are needed to meet evolving requirements, while at the same time continuing reduction of manufacturing costs is also important. .

Air bags or additional restraint systems are important safety features in many vehicles today. In the past, airbag systems were in the form of explosive chemicals, but they were expensive and, due to environmental and regeneration problems, recently a new type of inflator has been developed using shock absorbers made of steel tubes filled with argon gas, etc. This form is increasingly being used.

The shock absorber is a container that normally keeps the gas at high pressure and releases it to the airbag by a single or multiple stage explosion in the event of a vehicle crash. Therefore, the steel tube used as such a shock absorber at high expansion rates in a very short time. Therefore, compared with simple structures such as general high pressure cylinders, the steel tube is required to have excellent dimensional accuracy, good workability and weldability, and above all, have strong strength, robustness and good explosion resistance. Dimensional accuracy is also important to ensure that a very accurate volume of gas flows into the airbag.

Cold forming properties are very important in the annular members used to make shock absorbers because they form the final shape after the tube is made. Various shapes depending on the container arrangement will be obtained by cold forming. It is important to obtain a high pressure vessel without cold cracking and surface area defects after cold forming. Furthermore, it is essential to have very good robustness even at low temperatures after cold forming.

The steel described herein has very good weldability and does not require preheating or post-weld heat treatment prior to welding in airbag shock absorber applications. The carbon equivalent defined by the formula should be less than about 0.63% to achieve the required weldability:

Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15

As Ceq decreases, weldability increases. In a preferred embodiment of the invention, the carbon equivalent as defined above is less than about 0.60%, preferably less than about 0.56%, and most preferably less than about 0.52%, or about 0.48% to ensure better weldability. Is less than.

To produce gas containers, cold-drawn tubes made in accordance with the present invention are cut in length and then cold formed using various known techniques (such as crimping, swaging, etc.) to obtain the desired shape. Optionally, welded tubes can be used. The end cap and diffuser may then be welded to each end of the container by any suitable technique, such as friction welding, gas tungsten arc welding or laser welding, to produce the shock absorber. These welds are very important and require considerable labor and, in some cases, testing to ensure weld flawlessness through the development of high pressure vessels and airbags. These welds could break or fail, thus making the shock absorber flawless, and possibly the operability of the airbags observed.

The inflator is tested to ensure that the structural integrity of the inflator is maintained while the airbag is deployed. One such test is the so-called explosion test. This is a fracture-type test where the vessel is subjected to significantly higher internal pressures than expected during normal operation, ie air bag deployment. In this test, the inflator undergoes an increase in internal pressure until breakdown occurs.

By reviewing the explosive test results and studying the test canister specimens of these tests, it was found that crushing occurred through various alternative methods: soft crushing, brittle crushing, and sometimes a combination of these two approaches. Out of the ruptures exemplified by open protrusions (as indicated by exploding droplets) in soft fractures. The ruptured surface is inclined at about 45 ° to the tube outer surface and localized within the subject area. On the other hand, brittle fracture results in vertical cracks that do not stop along the length of the expander, indicating a brittle zone of the material. In this case, the fracture surface is normal to the tube outer surface. These two modes of fracture have distinct surfaces when observed by scanning electron microscopy-ripple is a characteristic of soft fracture, whereas cleavage is a sign of brittleness.

Occasionally, a combination of these two fracture modes can be observed and brittle cracks can develop from the soft fracture zone. Since the entire system, including the airbag inflator, can be used in vehicles operating in a wide variety of climates, it is important for the material to exhibit ductile behavior from a wide temperature range, from very low to warm temperatures.

Firstly, the present invention firstly has a high tensile strength (minimum UTS 145 ksi) and preferably ultra-high tensile strength (minimum UTS 160 ksi and possibly 175 ksi or 220 ksi), followed by a very high explosion pressure. It relates to certain novel low carbon alloy steels suitable for cold forming. Moreover, the steel has excellent low temperature robustness, which ensures ductile behavior at −60 ° C., ie has a ductile-to-brittle transition temperature (DBTT) lower than −60 ° C. and preferably as low as −100 ° C.

Secondly, the present invention also relates to a method for producing a steel tube which essentially comprises a novel rapid induction austenitization / fast quenching / quenching-free technique. In a preferred method, it is also by an ultra-fast water quenching step excluding any quenching step that produces a low carbon alloy steel suitable for cold forming with the highest tensile strength (minimum UTS 145 ksi and maximum 220 ksi) and consequently very high explosion pressure. There is an extremely fast induction austenitization. Moreover, the steel has excellent low temperature robustness, which ensures ductile behavior at −60 ° C., ie has a ductile-to-brittle transition temperature (DBTT) lower than −60 ° C. and preferably as low as −100 ° C.

The material of the invention is particularly useful as a component of a container for an automobile restraint system component, for example an automobile air bag inflator. The chemistry used to produce each of the steels described herein is novel and is then identified as Steel A, Steel B, Steel C, Steel D and Steel E, each of which is summarized in Table I below.

Test results with each of these steels in the novel rapid induction austenitization / fast quenching / quenching-free technique show surprising and varied results, of which five steel compositions are summarized in Table II below.

Preferred embodiments of the invention are described in detail below by way of example only with reference to the accompanying drawings.

1 is a core microstructure of high speed quenching in steel E. FIG.

2 shows an explosion test at −60 ° C. of high speed quenching in steel E. FIG.

3 shows the microstructure of normal quenching in steel E. FIG.

4 shows the core microstructure of high speed quenching in steel D. FIG.

5 shows an explosion test at −60 ° C. of high speed quenching in Steel D. FIG.

6 shows the microstructure of normal quenching in steel D. FIG.

While the present invention may be embodied in various forms, it is to be understood that the following describes the presently preferred embodiments as examples of the invention and is not intended to limit the invention to the specific embodiments described. .

The present invention relates to the material of a steel tube to be used in an embedded gas expander high pressure vessel. More particularly, the present invention provides a seamless high pressure tube having a guaranteed soft behavior at −60 ° C., ie, having a soft-to-brittle transition temperature lower than −60 ° C. and preferably as low as −100 ° C. A low carbon ultra high strength steel grade for application.

More particularly, the present invention relates to chemical compositions and methods for producing the material of seamless steel tubes to be used to make inflators.

A schematic description of the method of manufacturing a seamless low carbon ultra high strength steel is as follows:

1. Steel fabrication

2. steel casting

3. tube hot rolling

4. Hot rolled hollow finish work

5. Cold drawing

6. Austenitization by quenching (quenching-free)

7. Cold-drawn tube finishing work

One of the main purposes of the steel-making process is to refine iron by removing carbon, silicon, sulfur, phosphorus and manganese. In particular, sulfur and phosphorus are detrimental to steel because they deteriorate the mechanical properties of the material. Ladle metallurgy is used before and after the basic process to perform specific purification steps to allow for rapid processing in the basic steel manufacturing process.

The steel-manufacturing process is carried out under extremely clean runs to very low sulfur and phosphorus content, which is very important this time to achieve the high firmness required of the product. Therefore, in accordance with the guidelines of the ASTM E45 Standard-Standard-Worst Field Method (Method A), 2 or less-thin series-and 1 or less level-heavy series- Subject to the content level of. In a preferred embodiment of the invention, the maximum microcontent content measured according to the above standard is as follows:

In addition, extremely clean running conditions result in oversize contents of less than 30 μm in size. These contents are obtained by limiting the total oxygen content to 20 ppm.

An extremely clean run in the second metallurgy is carried out by boiling inert gases into the ladle to force the contents and impurities to float. The production of fluid slag capable of absorbing impurities and inclusions, and the modification of the size and shape of the inclusions by adding SiCa to the liquid steel, produce high quality steels with a low content of contents.

Example using low carbon, alloy steel

The chemical composition of the steel obtained is as follows, in each case "%" means "% by weight":

Carbon (C)

Carbon is an element that increases the strength of steel inexpensively, but when the content is less than 0.06%, it is difficult to obtain the desired strength. On the other hand, if the C content in the steel exceeds 0.18%, cold workability, weldability, and firmness decrease. Therefore, the C content ranges from 0.06% to 0.18%. Preferred C content ranges from 0.07% to 0.12% and more preferably 0.10 to 0.12%.

Manganese (Mn)

Mn is an effective element to increase the hardenability of steel, and thus manganese increases strength and robustness. If the content of manganese is less than 0.3%, it is difficult to obtain the desired strength, while if the content is more than 1.5%, a band structure appears and the tightness is reduced. Thus, the Mn content is 0.3% to 1.5% and the preferred Mn range is 0.60 to 1.40%.

Silicon (Si)

Si is an element that has an oxygen removing effect during the steel manufacturing process and also increases the strength of steel. If the Si content is less than 0.05%, the steel is easy to oxidize, while if it exceeds 0.50%, both the firmness and workability decrease. The Si content is therefore 0.05% to 0.50%., And the preferred Si range is 0.05% to 0.40%.

Sulfur (S)

S is an element that reduces the firmness of steel. Thus, the S content is limited to at most 0.015%. Preferred maximum value is 0.010%.

Phosphorus (P)

P is an element that reduces the firmness of steel. Thus, the P content is limited to a maximum of 0.025%. Preferred maximum value is 0.02%.

Nickel (Ni)

Ni is an element that increases the strength and robustness of steel, but it is very expensive, and therefore for cost, Ni is limited to a maximum of 0.70%. Preferred maximum value is 0.50%.

Chromium (Cr)

Cr is an effective element for increasing the strength, firmness, and corrosion resistance of steel. If chromium exceeds 1%, the firmness in the weld zone is significantly reduced. Therefore, the Cr content is limited to a maximum of 1.0%, and the preferred maximum content of Cr is 0.80%.

Molybdenum (Mo)

Mo is an effective element for increasing the strength of steel and contributes to slowing softening during quenching, but is very expensive. Therefore, the Mo content is limited to a maximum of 0.7% and the preferred Mo maximum content is 0.50%.

Vanadium (V)

V is an effective element for increasing the strength of steel even in small amounts, and slows softening during quenching. However, its ferroalloy is expensive and it is required to lower the maximum content. Therefore, V is limited to 0.3% at maximum, preferably 0.20% at maximum.

Preferred ranges of other elements not listed above are as follows:

Element weight%

Aluminum (Al) up to 0.10%

Niobium (Nb) up to 0.06%

Tin (Sn) up to 0.05%

Antimony (Sb) up to 0.05%

Lead (Pb) up to 0.05%

Arsenic (As) up to 0.05%

The remaining elements of the single ladle of steel used to produce the pipe or chamber are:

Sn + Sb + Pb + As ≤ 0.15% max

S + P ≤ 0.025

The next step is steel casting to produce solid steel bars that can be drilled and wound to form a seamless steel tube. The steel is cast into round solid steel strips of uniform diameter along the steel axis in the steel shop.

The solid cylindrical steel sheet of ultra high clean steel is heated to a temperature of about 1200 ° C. to 1300 ° C., which undergoes a rolling-mill process. Preferably the steel sheet is heated to a temperature of about 1250 ° C. and then passed through a rolling-mill. The steel sheet is preferably drilled using the known Mannessmann method, and then the length is substantially increased during hot rolling, while the outer diameter and wall thickness are substantially reduced. For example, a solid bar with an outer diameter of 148 mm is hot rolled into a hot-rolled tube with an outer diameter of 48.3 mm and a wall thickness of 3.25 mm.

The cross sectional area reduction, measured as the ratio of the cross section of the solid steel sheet to the cross sectional area of the hot rolling, is important for obtaining the refined microstructure necessary to achieve the desired mechanical properties. Therefore, the minimum cross sectional area reduction is about 15: 1, and the preferred and most preferred minimum cross sectional area reduction is about 20: 1 and about 25: 1, respectively.

The seamless hot-rolled tube of ultra-clean steel thus produced is cooled to room temperature. The seamless hot-rolled tube of ultra-high clean steel thus produced has a nearly uniform wall thickness both in the circumference of the tube and vertically along the tube axis.

The hot-rolled tube then passes through various finishing steps, for example, cut into lengths of 2 to 4 pieces, the ends of which are cut off, if necessary, calibrated in known rotary straightening devices, and As with tests or ultrasonic tests, they are tested non-destructively by one or more of various known techniques.

Then, the surface of each piece of hot-rolled tube is precisely conditioned for cold drawing. This conditioning involves immersing in an acid solution for washing and applying an appropriate layer of a brightening agent or reactive oil, such as known zinc phosphate and sodium stearate combinations. After surface conditioning, the seamless tube is cooled and pulled through an outer die having a diameter smaller than the outer diameter of the tube to be stretched. In most cases, the inner surface of the tube is also supported by an inner mandrel fixed to one end of the rod, so that the mandrel remains in close contact with the die during stretching. This stretching operation is carried out without the need to preheat the tube above room temperature.

The seamless tube is thus cold drawn at least once, and each pass reduces both the outer diameter and the wall thickness of the tube. The cold-drawn steel tube thus produced has a uniform outer diameter along the tube axis and a uniform wall thickness circumferentially around the tube and longitudinally along the tube axis. Such cold-rolled tubes preferably have an outer diameter of 10 to 70 mm and a wall thickness of preferably 1 to 4 mm.

The cold-rolled tube is then austenite at a temperature at least above the austenite temperature or Ac 3 (which is about 800 ° C. for certain chemistries described herein), preferably at a temperature of at least about 920 ° C. and at most 1050 ° C. Heat treatment in the furnace This maximum austenitization temperature is imparted to avoid grain agglomeration. This process can be carried out in a fuel furnace or in an induction furnace. The passage time in the furnace is highly dependent on the type of furnace used. It has been found that the high surface quality required for this application is better obtained when induction type furnaces are used. This is due to the nature of the induction process, where the transit time is very short and prevents oxidation. Preferably, the austenitization heating rate is about 100 ° C. per second, but more preferably at least about 200 ° C. per second. Extremely fast heating rates and, as a result, very short heating times are important for obtaining very good grain microstructure, which in turn ensures the required mechanical properties.

Moreover, a suitable filling factor, defined as the ratio of the circular region defined by the tube outer diameter to the circular region defined by the coil inner diameter of the induction furnace, is important for obtaining the required fast heating rate. The minimum fill factor is about 0.16 and the preferred minimum fill factor is about 0.36.

At or near the exit of the furnace the tube is expedited by a suitable quench fluid. The quench fluid is preferably water or a water-based quench solution. The tube temperature drops rapidly to ambient temperature, preferably at a speed of at least about 100 ° C. per second, more preferably at a speed of at least about 200 ° C. per second. This extremely fast cooling rate is crucial for obtaining complete microstructure deformation.

In the technique in which a quenching step is applied, the steel tube is then quenched at a temperature below AcI, with appropriate temperature and circulation time. Preferably, the quenching temperature is about 400 to 600 ° C, more preferably about 450 to 550 ° C. Optionally, the quenching temperature is between 200 ° C. and 600 ° C. and more preferably between 250 ° C. and 55 ° C. Immersion times should be long enough to ensure very good temperature uniformity, but if too long, the desired mechanical properties will not be achieved. This quenching step is preferably carried out in a protective reducing or neutral atmosphere to prevent the carbonization and / or oxidation of the tube.

In a preferred method, the quenching step is eliminated and only rapid quenching with water or water-based solutions as above is applied. In order to obtain high speed quenching, the following equipment is preferable but not necessary.

A quench line with a total capacity of 220 kg / h, followed by an induction furnace with the maximum power of the inductor set to 500 Kw. The head quencher applies 42 lines to 12 nozzles on each line. The water quench flow is set in the range of 10 to 60 m ³ / h and the advancing speed of the tube is adjusted to 5 to 25 / min. In addition, the pinch rollers are then equipped to create a rotation relative to the tube.

The ultra high strength steels thus produced are passed through various finishing steps, calibrated in known rotary straightening devices, and tested non-destructively by one or more of various known techniques. Preferably, for this kind of application, the tube must be tested by both known ultrasonic and electromagnetic techniques.

After heat treatment, the tubing can be chemically treated to obtain a tube with a desirable appearance and very low surface roughness. For example, the tube may be immersed in sulfuric acid or hydrochloric acid solution, phosphorylated with zinc phosphate, or oiled with petroleum-based oil, water-based oil or mineral oil.

The steel tubes obtained by the first and second described methods have the following minimum mechanical properties:

Yield strength at least about 110 ksi (758 MPa)

Tensile Strength Minimum Approx. 145 ksi (1000 MPa)

At least 9% height

Yield strength, tensile strength and elongation can be performed according to the methods disclosed in standard ASTM E8. For tensile strength, full-size specimens are preferred for evaluating the entire annular compartment.

The spread test meets the requirements of 39 DOT section 178.65 of the 49 CFR. Therefore, when the tube section is unfolded with a 60 ° angled V-shaped tool, it does not crack until the opposite side is six times the thickness of the individual tube wall. This test will be fully met by the developed steel.

In order to obtain a good balance between strength and robustness, the austenite grain size of the preceding (sometimes expressed electronically) is preferably 7 or less, more preferably 9 or less, as measured according to the ASTM E-112 standard. . This is done thanks to the extremely short heating cycle during austenitization.

The steel tube obtained according to the described method must have the properties mentioned in order to meet the requirements mentioned in the present invention.

Industry demand continues to drive the importance of crudeness requirements further. The present invention has a good visible appearance, for example with a surface finish of up to 3.2 microns of finished tubing on both the outer and inner surfaces. This requirement is achieved through cold drawing, short austenitization time, reducing or neutral atmospheric quenching, and sufficient surface chemical conditioning at various stages of the process.

The water explosion pressure test can be performed by sealing the end of the tube compartment and welding a flat steel sheet to the end of the tube. It is important that the 300 mm tube compartment remains unconstrained to show full circumferential stress. Pressurization of the tube compartment may be carried out by injecting oil, water, alcohol or mixtures thereof.

Explosion test pressure requirements depend on the tube size. When the explosion is tested, the ultra high strength steel seamless tube has a guaranteed ductile behavior at -60 ° C. Tests performed on the resulting samples indicate that this grade has a guaranteed soft behavior at -60 ° C and a soft-to-brittle transition temperature of -60 ° C or lower.

The inventors found that a more representative confirmation test is an explosion test performed at ambient temperature and low temperature, instead of the Charpy impact test (according to ASTM E23). This is because relatively thin wall thicknesses and small outer diameters are applied to these products, so that standard ASTM specimens for Charpy impact testing are not machined from the tube in the transverse direction. Moreover, in order to obtain Charpy impact probes smaller than this standard, flattened strains have to be applied to bent tube probes. This has the effect of being sensitive to steel mechanical properties, in particular impact strength. Therefore, a representative impact test is not obtained with this procedure.

Examples using optional, low carbon, low alloyed steels

Applicants have found that quenching free high speed quenching is a critical aspect of the present invention. Less alloyed and less expensive steel than the prior art may meet or exceed the criteria discussed above if treated by special heating and rapid quenching.

The new steels A, B, C, D and E, as defined above, are optional steels analyzed using the appropriate method, where a high speed induction furnace, which is austenitized by rapid quenching, was used instead of adding a quenching step. Surprisingly, when a control test for these particular new steels, ie, a quench slower than a high speed, ie, a normal quenching process, was applied, or as described above, a quenching step was applied, the test showed quite poor characteristics.

High speed quench and quench-free process optionally comprising low cost steel according to a preferred method

The parameters used in the rapid quench test for steel E samples were as follows: water flow rate 40 m ³ / hr; Tube advancement speed 20 m / min; Inductor power 80%; Austenitization temperature of 880 to 940 ° C; Aiming 920 °; Martensite deformation was observed on the OD surface and core material.

1 shows a 100% martensite modified core material in steel E. FIG.

Steel E has a chemistry similar to that of low alloy SAE 1010 grade steel and, when fast quenched, does not achieve minimum expectations.

The test results are as follows:

On the other hand, the explosion test at low temperature (-60 ℃) was carried out to observe the crack behavior and type. 2 shows the exploded samples tested for steel E. FIG. Both exhibited soft behavior.

Control tests involving a normal quench process were performed on steel E, with the following results:

3 shows the core structure of steel E using a normal quench process. Some ferrite structure was observed along the wall thickness.

Steel D was found to be very promising as it exhibited high performance relative to cost. Steel D was chosen to fabricate the tubing according to the preferred method. The measured chemical composition of the sample of Steel D used in the rapid quench test is as follows:

The parameters used in the fast quench test on a sample of Steel D are as follows:

The quenching process was performed while controlling the austenite temperature to 920-940 ° C.

Water flow rate 40 m ³ / h

Tube Advance Speed 1Om / Min

62% of total capacity of inductor power (500 Kw)

Rotation to the tube was provided at a pinch roll angle of 17 °.

The fast quench test results for a sample of steel D are as follows:

4 shows a high speed quenched steel D microstructure showing 100% martensite and fully quenched strain.

On the other hand, explosion tests at low temperatures (-60 ° C.) were performed to observe the behavior and type of cracks. 5 shows exploded samples tested for steel D. FIG. Both exhibited soft behavior.

Control tests were performed on Steel D, including the normal quench process, with the following results:

6 shows the core structure for steel D using a normal quench process.

Steel B was selected to fabricate the tubing according to the present invention. The measured chemical composition of the sample of Steel B used in the high speed quench test is as follows:

The parameters used for the rapid quench test on a sample of Steel B were as follows:

The quenching process was performed while controlling the austenite temperature to 920-940 ° C.

Water flow rate 40 m ³ / h

Tube Advance Speed 1Om / Min

70% of total capacity of inductor power (500 Kw)

Rotation to the tube was provided at a pinch roll angle of 17 °.

The fast quench test results for a sample of steel B are as follows:

On the other hand, an explosion test at low temperature (-60 ° C.) on steel B was performed to observe the behavior and type of cracking, both of which showed ductile behavior.

Steel A was selected to fabricate the tubing according to the present invention. The measured chemical composition of the sample of Steel A used in the rapid quench test is as follows:

The parameters used for the fast quench column for a sample of Steel A were as follows:

The quenching process was performed while controlling the austenite temperature to 920-940 ° C.

Water flow rate 50 m ³ / h

Tube Advance Speed 2Om / Min

90% of total capacity of inductor power (500 Kw)

Rotation to the tube was provided at a pinch roll angle of 17 °.

The fast quench test results for a sample of steel A are as follows:

On the other hand, explosion tests at low temperatures (-60 ° C and -100 ° C) on steel A were performed to observe the behavior and type of cracks, both of which showed ductile behavior.

Contrast test by high speed quench and subsequent quenching process using optional low cost steel

It was found that once a sample of steel D produced surprising mechanical value after using the high speed quenching according to the invention, the quenching was then performed to determine the effect of adding quenching to the mechanical properties.

Quenching heat treatment was performed at 580 ° C. for a total of 15 minutes. The UTS average was 116 Ksi (805 MPa), which did not live up to expectations.

Preferred embodiments of the invention have been shown and described in accordance with the description and feasibility requirements of 35 USC § 112, and it is to be understood that the scope of the invention is not limited to any of the embodiments described, and that the appended claims are limited only by the scope. do.

Claims (48)

Essentially about 0.06% to about 0.18% carbon; About 0.5% to about 1.5% manganese; About 0.1% to about 0.5% silicon; Up to about 0.015% sulfur; Up to about 0.025% phosphorus; Up to about 0.50% nickel; About 0.1% to about 1.0% chromium; About 0.1% to about 1.0% molybdenum; Vanadium about 0.01% to about 0.10%; About 0.01% to about 0.10% titanium; About 0.05% to about 0.35% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15 weight percent of the remaining elements; And a low carbon alloy steel tube consisting of the remaining iron and accidental impurities, wherein the steel tube has a tensile strength of at least about 145 ksi and a ductile-to-brittle transition temperature of -60 ° C. or less. The method of claim 1, wherein the steel tube consists essentially of about 0.07% to about 0.12% carbon; About 1.00% to about 1.40% manganese; About 0.15% to about 0.35% silicon; Up to about 0.010% sulfur; Up to about 0.015% phosphorus; Up to about 0.20% nickel; About 0.55% to about 0.80% chromium; About 0.30% to about 0.50% molybdenum; Vanadium about 0.01% to about 0.07%; About 0.01% to about 0.05% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15 weight percent of the remaining elements; And low carbon alloy steel tubes consisting of the remaining iron and accidental impurities. The method of claim 1, wherein the steel tube comprises essentially about 0.08% to about 0.11% carbon; About 1.03% to about 1.18% manganese; About 0.15% to about 0.35% silicon; Up to about 0.003% sulfur; Up to about 0.012% phosphorus; Up to about 0.10% nickel; About 0.63% to about 0.73% chromium; About 0.40% to about 0.45% molybdenum; Vanadium about 0.03% to about 0.05%; About 0.025% to about 0.035% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; About 0.15% by weight of the remaining atoms; And low carbon alloy steel tubes consisting of the remaining iron and accidental impurities. The low carbon alloy steel tube of claim 1, wherein the steel tube has a yield strength of at least 125 ksi. The low carbon alloy steel tube of claim 1, wherein the steel tube has a yield strength of at least about 135 ksi. The low carbon alloy steel tube of claim 1, wherein the steel tube has an elongation at break of at least about 9%. The low carbon alloy steel tube of claim 1, wherein the steel tube has a hardness of no greater than about 40 HRC. The low carbon alloy steel tube of claim 1, wherein the steel tube has a hardness of no greater than about 37 HRC. The low carbon alloy steel tube of claim 1, wherein the steel tube has a carbon equivalent of less than about 0.63% and the carbon equivalent is determined according to the following equation: Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15. 10. The low carbon alloy steel tube of claim 9, wherein the steel tube has a carbon equivalent of less than about 0.60%. 10. The low carbon alloy steel tube of claim 9, wherein the steel tube has a carbon equivalent of less than about 0.56%. The steel tube of claim 1 wherein the steel tube has a maximum fines content of 2 or less-a thin series-and 1 or less-a heavy series-measured according to ASTM E45 standard—worst-field method (method A). Low carbon alloy steel tube. The low carbon alloy steel tube of claim 1, wherein the steel tube has a maximum fines content as measured in accordance with ASTM E45 Standard-Worst Field Method (Method A):

The low carbon alloy steel tube of claim 13, wherein an oversize inclusion component of 30 μm or less is obtained. 15. The low carbon alloy steel tube of claim 14, wherein the total oxygen content is limited to 20 ppm. The low carbon alloy steel tube of claim 1, wherein the tube has a seamless appearance. An embedded gas expander high pressure vessel comprising a low carbon alloy steel tube according to claim 1. An automotive airbag inflator comprising a low carbon alloy steel tube according to claim 1. Essentially about 0.08% to about 0.11% carbon; About 1.03% to about 1.18% manganese; About 0.15% to about 0.35% silicon; Up to about 0.003% sulfur; Up to about 0.012% phosphorus; About 0.10% nickel; About 0.63% to about 0.73% chromium; About 0.40% to about 0.45% molybdenum; Vanadium about 0.03% to about 0.05%; About 0.025% to about 0.035% titanium; About 0.15% to about 0.30% copper; About 0.010% to about 0.050% aluminum; Up to about 0.05% niobium; Up to about 0.15 weight percent of the remaining elements; And a low carbon alloy steel tube consisting of the remaining iron and accidental impurities, wherein the steel tube has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, at least about 9% elongation at break, and not more than about 37 HRC. Low carbon alloy steel tube having a hardness and a ductile-to-brittle transition temperature of -60 ° C. or less. 20. The low carbon alloy steel tube of claim 19, wherein the tube has a seamless appearance. 20. Built-in gas expander high pressure vessel comprising a low carbon alloy steel tube according to claim 19. An automotive airbag inflator comprising a low carbon alloy steel tube according to claim 19. A method of making long steel tubing for an embedded gas expander high pressure vessel, wherein the process consists essentially of about 0.06% to about 0.18% carbon, about 0.5% to about 1.5% manganese, and about 0.1% to about silicon About 0.5% by weight, up to about 0.015% sulfur, up to about 0.025% phosphorus, up to about 0.50% nickel, about 0.1% to about 1.0% chromium, about 0.1% to about 1.0% molybdenum, about vanadium 0.01 wt% to about 0.10 wt%, titanium about 0.01 wt% to about 0.10 wt%, copper about 0.05 wt% to about 0.35 wt%, aluminum about 0.010 wt% to about 0.050 wt%, niobium max. About 0.05 wt% Making a long piping from a steel material consisting of up to about 0.15% by weight of element, and the remainder of iron and accidental impurities; Cold-drawing the steel tubing to obtain the desired dimensions; Austenitizing the cold-drawn steel tube in an induction-type austenitization furnace by heating to at least Ac3 temperature at a heating rate of at least about 100 ° C./sec; After the heating step, quenching the steel tubing at a rate of at least about 100 ° C./sec in the quench fluid until the tubing reaches nearly ambient temperature; And after the quenching step, quenching the steel tubing at a temperature below AcI for about 2-30 minutes. The steel tubing of claim 23, wherein the resulting steel tubing consists essentially of: about 0.07% to about 0.12% carbon, about 1.00% to about 1.40% manganese, about 0.15% to about 0.35% silicon, up to about sulfur 0.010% by weight, phosphorus up to about 0.015%, nickel up to about 0.20%, chromium about 0.55% to about 0.80%, molybdenum about 0.30% to about 0.50%, vanadium about 0.01% to about 0.07% , About 0.01% to about 0.05% titanium, about 0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% by weight of the remaining elements, and Method of production consisting of the remaining iron and accidental impurities. 24. The steel tubing of claim 23 wherein the steel tubing produced is essentially: from about 0.08% to about 0.11% carbon, from about 1.03% to about 1.18% manganese, from about 0.15% to about 0.35% silicon, up to about sulfur 0.003% by weight, up to about 0.012% by weight, up to about 0.10% by weight of nickel, about 0.63% to about 0.73% by weight of chromium, about 0.40% to about 0.45% by weight of molybdenum, about 0.03% to about 0.05% by weight of vanadium About 0.025% to about 0.035% titanium, about 0.15% to about 0.30% copper, about 0.010% to about 0.050% aluminum, up to about 0.05% niobium, up to about 0.15% by weight of the remaining elements, and Method of production consisting of the remaining iron and accidental impurities. The method of claim 23, wherein the finished steel tubing has a yield strength of at least about 125 ksi. The method of claim 23, wherein the finished steel tubing has a yield strength of about 135 ksi. The method of claim 23, wherein the finished steel tubing has a tensile strength of at least about 145 ksi. The method of claim 23, wherein the finished steel tubing has an elongation at break of at least about 9%. The method of claim 23, wherein the finished steel tubing has a hardness not greater than about 40 HRC. The method of claim 23, wherein the finished steel tubing has a hardness not greater than about 37 HRC. The method of claim 23, wherein the finished steel tubing has a draw-to-brittle transition temperature of −60 ° C. or less. 24. The method of claim 23, wherein in the austenitic heating step, the steel tubing is heated to a temperature of about 920-1050 ° C. The method of claim 33, wherein in the austenitic heating step, the steel tubing is heated at a rate of at least about 200 ° C./sec. The method of claim 23, wherein in the quenching step, the steel tubing is cooled at a rate of at least about 200 ° C./sec. 24. The method of claim 23, wherein in the quenching step, the steel tubing is quenched at a temperature of about 400-600 ° C. The method of claim 36, wherein in the quenching step, the steel tubing is quenched for about 4-20 minutes. The method of claim 23, wherein the quenched steel tubing further comprises a finishing step that is pickled with dilute acidic water, phosphorylated, and oiled. A method of making long steel tubing for an embedded gas expander high pressure vessel, wherein the process consists essentially of about 0.08% to about 0.11% carbon, about 1.03% to about 1.18% manganese, and about 0.15% silicon to About 0.35% by weight, up to about 0.003% by sulfur, up to about 0.012% by weight, up to about 0.10% by weight of nickel, about 0.63% to about 0.73% by weight of chromium, about 0.40% to about 0.45% by weight of molybdenum, about vanadium 0.03% to about 0.05%, titanium about 0.025% to about 0.035%, copper about 0.15% to about 0.30%, aluminum about 0.010% to about 0.050%, niobium up to about 0.05%, rest Making a long piping from a steel material consisting of up to about 0.15% by weight of element, and the remainder of iron and accidental impurities; Cold-drawing the steel tubing to obtain the desired dimensions; Austenitizing the cold-drawn steel tube in an induction-type austenitization furnace by heating to a temperature of about 920-1050 ° C. at a heating rate of at least about 200 ° C./sec; After the heating step, quenching the steel tubing in a water-based quench solution at a cooling rate of at least about 200 ° C./sec until the tubing reaches near ambient temperature; And after the quenching step, quenching the steel tubing at a temperature of 450-550 ° C. for about 4-20 minutes, and in the finishing step, the quenched steel tubing is washed with dilute oxygen, phosphorylated, And oiled, where the finished steel tubing has a yield strength of at least about 135 ksi, a tensile strength of at least about 145 ksi, an elongation at break of at least about 9%, a hardness not greater than 37 HRC, ductile-to- The brittle transition temperature is below -60 ℃, and has a good surface appearance. A method of making long steel tubing for an embedded gas expander high pressure vessel, wherein the process consists essentially of about 0.06% to about 0.18% carbon, about 0.3% to about 1.5% manganese, and about 0.05% to about silicon About 0.5% by weight, up to about 0.015% sulfur, up to about 0.025% phosphorus, and at least one of the following elements: up to about 0.30% vanadium, up to about 0.10% aluminum, up to about 0.06% niobium, up to chromium A long pipe is made from a steel material comprising about 1% by weight, up to about 0.70% by weight of nickel, up to about 0.70% by weight of molybdenum, up to about 0.35% by weight of copper, up to about 0.15% by weight of the remaining elements, and the rest of iron and accidental impurities Doing; Cold-drawing the steel tubing to obtain the desired dimensions; Austenitizing the cold-drawn steel tube in an induction-type austenitization furnace by heating to at least Ac3 temperature at a heating rate of at least about 100 ° C./sec; After the heating step, quenching the steel tubing at a rate of at least about 100 ° C./sec in the quench fluid until the tubing reaches nearly ambient temperature; Wherein the steel tubing has a tensile strength of at least about 145 ksi and a ductile-to-brittle transition temperature of -60 ° C. or less. The steel tubing of claim 40 wherein the produced steel tubing is essentially from about 0.07% to about 0.12% carbon, from about 0.60% to about 1.40% manganese, from about 0.05% to about 0.40% silicon, sulfur max. About 0.010% by weight, up to about 0.02% by weight, and at least one of the following elements: vanadium up to about 0.20%, aluminum up to about 0.07%, niobium up to about 0.04%, chromium up to about 0.8%, nickel max About 0.50 wt%, molybdenum up to about 0.50 wt%, copper up to about 0.35 wt%, remaining elements up to about 0.15 wt%, and the remainder of iron and accidental impurities, wherein the steel tube has a tensile strength of at least about 160 ksi And a soft-to-brittle transition temperature of -60 ° C. or less. The method of claim 40, wherein the steel tube has a carbon equivalent of less than about 0.52% and the carbon equivalent is determined according to the following formula: Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15. The method of claim 41, wherein the steel tube has a carbon equivalent of less than about 0.48% and the carbon equivalent is determined according to the following formula: Ceq =% C +% Mn / 6 + (% Cr +% Mo +% V) / 5 + (% Ni +% Cu) / 15. 41. The method of claim 40, wherein the finished steel tubing has an elongation at break of at least about 9%. 41. The method of claim 40, wherein in the austenitic heating step, the steel tubing is heated to a temperature of about 860-1050 ° C. The method of claim 40, wherein in the austenitic heating step, the steel tubing is heated at a heating rate of at least about 200 ° C./sec. The method of claim 40, wherein in the quenching step, the steel tubing is cooled at a rate of at least about 200 ° C./sec. A method of making long steel tubing for an embedded gas expander high pressure vessel, wherein the process consists essentially of about 0.07% to about 0.12% carbon, about 0.60% to about 1.40% manganese, about 0.05% to about silicon About 0.40% by weight, up to about 0.010% by sulfur, up to about 0.02% by weight, up to 0.20% by vanadium, up to about 0.07% by weight of aluminum, up to about 0.04% by weight of niobium, up to about 0.8% by weight of chromium, up to about nickel Preparing a long tubing with a steel material consisting of 0.50 wt%, molybdenum up to about 0.50 wt%, copper up to about 0.35 wt%, remaining elements up to about 0.15 wt%, and the remaining iron and accidental impurities; Cold-drawing the steel tubing to obtain the desired dimensions; Austenitizing the cold-drawn steel tube in an induction-type austenitization furnace by heating to a temperature of about 860-1050 at a heating rate of at least about 200 ° C./sec; After the heating step, quenching the steel tubing in the water-based quench solution at a rate of at least about 200 ° C./sec; Wherein the finished steel tubing has a tensile strength of at least about 160 ksi, an elongation at break of at least about 9%, and a ductile-to-brittle transition temperature of at most -60 ° C and preferably at most -100 ° C. Phosphorus manufacturing method.

Images