Acid steel takes its name from the fact that it is made in a furnace lined with a siliceous material, acid in character, while a basic steel is made in a furnace lined with basic material. It should be remembered that an acid is the opposite of a base, and that they neutralise one another. The basic lining of the furnace is able to rid the steel therein of most of the phosphorus and sulphur forming basic slags, but an acid lining cannot do this. From this it follows that materials containing phosphorus and sulphur can be used in the basic process, but this cannot be done in the acid process, the material having to be selected, in other words, a better quality is used. Opinions then differ as to whether it is better to use raw materials that do contain phosphorus or sulphur, or both, and eliminate them in the process, or by using selected materials, to never have had them present at all. There are obviously larger supplies of raw materials suitable for steel making that do contain phosphorus, or sulphur, or both, than supplies that are free of these two impurities.

The general trend of opinion appears to be that in the case of good quality acid and basic steels, one is as reliable as the other, but in the case of low quality steels the basic steel is likely to be the worse, this resulting from the fact that generally, where strength is required rather than ductility, then acid steel is called for in important specifications, hut where low strength and high ductility is required, then basic steel is allowed. Expert opinion still differs on the subject of acid as against basic steels, and possibly always will differ but certainly the use of basic steel is increasing faster than that of acid steel, and not altogether on account of its lower price.

Steels : Casehardening

The necessarv treatment for case-hardening of certain steels is as follows.

birth Carbon Case-hardening Steel (Guaranteed Analysis).-

Minimum Ultimate Tensile, 32 tons per sq. in.

Treatment

Forging-F o r g i n g should be carried out at a temperature not exceeding 1200° C.

Machining-This steel is easily machined in the rolled or forged condition.

Cementing-Pack the parts in a close box and heat to 900° C. I The time to maintain at this temperature varies according to the depth of case required, whether j surfaces are machined or left as forged, etc., and should be determined by experiment. After soaking, parts may be either left to cool in the box or withdrawn into the air.

Refining the Core-Heat up to 900° C. Maintain at this temperature for 20 minutes and quench in water.

Hardening-Heat up to 760° C. and quench in water.

Grinding-It is advisable to point out that final grinding should be done wet, to avoid the possibility of local heating and resultant soft patches.

Firth 2% Nickel Case-hardening Steel (Guaranteed Analysis).-

Minimum Ultimate Tensile, 35 tons per sq. in.

Treatment

Forging - Forging should be carried out at a temperature between 900° C. and 1200° C. This is a steel which forges readily, and requires no special precautions in handling.

Machining-This steel is easily machined in the rolled or forged condition. If, in certain cases, it is found difficult to obtain a high finish in this condition, the steel may be heated to 900° C. and quenched in oil. Such heating will not affect the subsequent case-hardening operation.

Cementing-Pack the parts in a close box and heat to 900° C. The time to maintain this temperature varies according to the depth of case required, whether surfaces are machined or left as forged, etc., and should be determined by experiment. After soaking, parts may be either left to cool in the box or withdrawn into the air.

Refining the Core-Heat up to 900° C. Maintain at this temperature for 20 minutes and quench in water or oil.

Hardening-Heat up to 760° C. and quench in water.

Grinding- It is advisable to point out that final grinding should be done wet to avoid the possibility of local heating and resultant soft spots.

FMh 5% Nickel Case-hardening Steel (Guaranteed Analysis).-

Minimum Ultimate Tensile. 45 tons per sq. in.

Treatment

Forging- Forging should be carried out at a temperature between 900° C. and 1150°C. A certain degree of care is necessary in forging this Steel, owing to its high nickel content, and care must be taken not to exceed the above maximum temperature.

Machining -This Steel is easily machined in the rolled or forged condition unless very thin in sectional area. In that case it is advisable before machining to heat the article up to 830° C. and cool in air.

Cementing-Pack the parts in a close box and heat to 900° C. The time to maintain this temperature varies according to the depth of case required, whether surfaces are machined or left as forged, etc., and should be determined by experiment. After soaking, parts may be either left to cool in the box or withdrawn into the air.

Refining the Core-Heat up to 830° C. Maintain at this temperature for 20 minutes and quench in water or oil.

Hardening-Heat up to 760° C. and quench in water.

Note

A variation of this temperature by 20 or 30 degrees above or below will alter considerably the mechanical properties of the core. In order to reduce to a minimum the tendency to distortion of delicate parts, the refining process may be omitted. Heat instead to 770° C. and quench in water.

Grinding-Final grinding should be done wet to avoid the possibility of local heating and resultant soft patches. (Thos. Firth & Sons Ltd.)