Metal treatment – Compositions – Heat treating
Patent
1989-03-14
1990-05-08
Yee, Deborah
Metal treatment
Compositions
Heat treating
148 12B, 148 12F, C21D 800
Patent
active
049235281
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for manufacturing rolled steel products, especially structural steels such as, for example, tension steels.
With respect to construction steels (heat treated steels) such as, for example, tension steels, high demands are placed with regard to mechanical properties. Tension steels are used in building construction as tensioning members for pre-stressed concrete, as anchor steels for earth and rock anchors, as concrete form anchors, for suspension cables for suspension bridges, cable ropes for cable rope bridges, staying and the like. For a portion of these applications tension steels, preferably with rod shaped across section are used in the strength class with yield points between 800 and 1000 N/mm.sup.2 (0,2-limit) and tensile strengths between 1100 and 1300 N/mm.sup.2. As to measurements, diameters from 12 to 50 mm, especially from 20 to 40 mm, come into question. This involves tension steels with smooth outer surfaces or steels with for example screw shaped inclined ribs. Other possible realizations for tension steels are wires and sheet steel.
Tension steels along with static strength must also possess a very high elastic limit and a good ductility. In the case of threaded tension steels, that is such to which a threaded anchor can be applied, a high wear resistance for the outer surface as well as resistance to corrosion is also important Further important requirements are good relaxation properties as well as an adequately high fatigue loading resistance. Rod shaped tension steels with diameters between about 12 and 50 mm are hot rolled to increase the yield point, subsequently stretched and then annealed to remove stress. According to these methods indeed the lesser requirements of the prescribed standards can be met, but the process is also with respect to the steel composition (typical analysis in W% (Weight Percentage): C 0.75, Si 0.80, Mn 1.50, P 0.020, S0.020, V 0.25) and the carrying out of the method quite expensive and associated with high production costs. Beside numerous production steps, residual hydrogen and metallurgical segregation represent for this steel a big problem. The disadvantageous effect of cracks appearing during the stretching, as also of cracks which occur later, and the general susceptibility to corrosion of such tension steel are known. The production disturbing high amount of rejects (scrap) in the plant represents another substantial cost factor.
A method for manufacturing rolled steel products, especially threaded tension steels and the like, is known from DE-OS 34 31 008, in which the steel with a C-content of from 0.50 to 0.80 W%, a Si-content of from 0.20 to 0.60 W%, and a Mn-content of from 0.30 to 0.80 W%, after hot rolling is cooled at the output side of the finishing equipment from the rolling heat, especially by means of water (in principle cooling gas comes into question), so that a quenching of the outer surface takes place such that the material in a peripheral zone is converted directly and entirely into martensite, while the heat which remains in the core zone during the subsequent cooling effects an annealing of the martensitic peripheral zone not beyond the range of the intermediate stage.
In accordance with this method it is possible to use starting compositions readily represented metallurgically and of cost effective analysis for the manufacture of a tension steel which is resistant to corrosion and having a wear resistant outer surface, which reduces the danger of mechanical damage and suits the steel to the application of threads. The tension steel obtained through this method exhibits moreover, along with a high yield point and a high strength, a high ductility or toughness above all at high temperatures, and it possesses along with low relaxation a high fatigue strength.
From LU-A-65 413 a method for manufacturing a non-heat treated steel is known, in which after the cooling a cold working is carried out with a following annealing. Since in the case of such steel, no metastable phase in the form of martensite appe
REFERENCES:
patent: 4203783 (1980-05-01), Economopoulos et al.
Richartz Erich
Russwurm Dieter
Aicher Max
Yee Deborah
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