Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Patent
1997-09-04
1999-11-09
Yee, Deborah
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
420 38, C22C 3842
Patent
active
RE0363820
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is concerned with the precipitation-hardenable martensitic chromium-nickel stainless steels, more especially those which are hardenable in a simple heat-treatment. More particularly, the concern is with the martensitic chromium-nickel stainless steels which are hardened by a simple heat-treatment at comparatively low temperature.
SUMMARY OF THE INVENTION
One of the objects of the invention is the provision of a martensitic chromium-nickel stainless steel which works well not only in a steelplant during e.g. rolling and drawing but also in the form of rolled and drawn products, such as strip and wire, readily lends itself to a variety of forming and fabrication operations, such as straightening, cutting, machining, punching, threading, winding, twisting, bending, and the like.
Another object is the provision of a martensitic chromium-nickel stainless steel which not only in the rolled or drawn condition but also in a hardened and strengthened condition offers very good ductility and toughness. A further object of the invention is the provision of a martensitic chromium-nickel stainless steel which, with its combination of very high strength and good ductility, is suitable for forming and fabrication of products such as springs, fasteners, surgical needles, dental instruments, and other medical instruments, and the like.
Other objects of the invention will in part be obvious and in part pointed out during the course of the following description.
DETAILED BACKGROUND OF PREFERRED EMBODIMENTS
Presently, many types of alloys are used for the forming and fabrication of the above mentioned products. Some of these alloys are martensitic stainless steels, austenitic stainless steels, plain carbon steels and precipitation-hardenable stainless steels. All these alloys together offer a good combination of corrosion resistance, strength, formability and ductility, but one by one they have disadvantages and can not correspond to the demands of today and in future on alloys used for the production of the above mentioned products. The demands are better material properties both for the end-user of the alloy, i.e. higher strength in combination with good ductility and corrosion resistance, and for the producer of the semi-finished products, such as strip and wire, and the producer of the finished products, mentioned above, i.e, properties such as e.g. that the material readily can be formed and fabricated in the meaning that the number of operations can be minimized and standard equipment can be used as long as possible, for the reduction of production cost and production time.
Martensitic stainless steels, e.g. the AISI 420-grades, can offer strength, but not in combination with ductility. Austenitic stainless steels, e.g. the AISI 300-series, can offer good corrosion-resistance in combination with high strength and for some applications acceptable ductility, but to achieve the high strength a heavy cold-reduction is needed and this means that also the semifinished product must have a very high strength and this further means that the formability will be poor. Plain carbon steels have a low corrosion resistance, which of course is a great disadvantage if corrosion resistance is required. For the last group. precipitation--hardenable stainless steels, there are numerous different grades and all with a variety of properties. However, they do have some things in common, e.g. most of them are vacuum--melted in a one-way or more commonly a two-way process in which the second step is a remelting under vacuum--pressure. Furthermore a high amount of precipitation--forming elements such as aluminium, niobium, tantalum and titanium is required and often as combinations of these elements. With "high" is meant >15% A high amount is beneficial for the strength, but reduces the ductility and formability. One specific grade that is used for the above mentioned products and which will be referred to in the description is according to U.S. Pat. No. 3.408,178, now expired. This gra
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Patent Abstracts of Japan, vol. 12, No. 387, C536, Abstract of JP63-134648, (Kobe Steel Ltd) Jun. 7, 1988.
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Sandvik AB
Yee Deborah
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