1 Purpose and application of steel St3
Steel grade St3 – that's what he calls her GUEST 380-2005 – refers to carbon steels of ordinary quality. More often it is called simply St3 steel. But not “steel 3” and no “steel grade 3” – so called high-quality carbon steels according to GOST 1050-88, eg, “steel grade 20” and often – “steel 20”.
Steel grade St3 is intended for the manufacture of hot-rolled steel - section, shaped, thick-leaved, thin-sheet, as well as pipes, forgings and stampings, tapes, wire, hardware.
2 Chemical composition of steel St3 in accordance with GOST 380-2005
2.1 Alloying elements:
2.2 Impurities, no more:
– chromium: 0,30 %;
– nickel: 0,30 %;
– copper: 0,30 %;
– sulfur: 0,005 %;
– phosphorus: 0,04 %;
– nitrogen: 0,10 %.
2.3 Degree of deoxidation of steel St3
According to the method of deoxidation, St3 steel is subdivided into:
– calm (manganese deoxidation, silicon and aluminum);
– boiling (deoxidation only with manganese) and
– semi-calm (deoxidation with manganese and aluminum).
The degree of deoxidation is indicated in the designation of steel by the letters "cn", "Kp" and "ps" respectively.
In terms of chemical composition, boiling steel differs from a calm one., which contains almost no silicon (less 0,05 %). Calm steel contains silicon from 0,15 to 0,30 %. Since boiling steel contains more oxygen, than calm steel, then it is worse in quality, than calm.
Semi-quiescent steel occupies an intermediate position in quality between boiling and quiescent steels..
2.4 Deoxidation of steel St3
Steel deoxidation - removal process from liquid steel, the oxygen in it. Oxygen is a harmful impurity, deteriorating the mechanical properties of the metal.
Deoxidation of steel consists in reducing the solubility of oxygen in steel by additives of deoxidizing elements and creating conditions for the possible complete removal of the resulting deoxidation products from liquid steel.
Manganese is mainly used for deoxidation of steels., silicon and aluminum. Manganese is a relatively weak deoxidizing agent. Silicon is a stronger deoxidizer, than manganese. Aluminum is the strongest steel deoxidizer.
3 Steel designation St3: old and new
3.1 Steel designation St3 in accordance with GOST 380-2005
Strictly speaking, GUEST 380-2005 does not provide for the designation of steel St3 in such a "pure" form "St3" - without the letters "kp", «Ps» and «sp». This standard defines steel grades St3kp, St3ps, St3sp, as well as their modifications with a high manganese content - St3Gsp and St3Gps. The use of the designation of steel St3 without accompanying letters is not provided for by the standard. Moreover, in GOST 380-2005 indicated, what if the order does not indicate the degree of deoxidation of steel, then it is set by the manufacturer. By the way, the cheapest to manufacture is boiling steel.
Full designation of any steel grade according to GOST 380-2005, that is, which must be specified in the order, looks like, eg, in the following way:
St3Gsp GOST 380-2005
St.: designation of carbon steel of ordinary quality;
3: conditional steel grade number (all of them in GOST 380-2005 seven, depending on its chemical composition - 0, 1, 2, 3, 4, 5, 6);
D: the letter G is present in the designation, if the mass fraction of manganese in steel exceeds 0,8 %;
Mr.: degree of steel deoxidation.
true, looks like, the practice has developed, when steel St3 is understood as St3sp. but, as we saw, GUEST 380-2005 does not formally envisage this.
3.2 Obsolete designations of steel St3
There are obsolete designations of steel St3, eg, VSt3ps5, and with links to the editions of GOST 380 from 1971, 1988, 1994 and even 1960 years, and that and 1950 of the year!
GUEST 380-1971 provided for the supply of steels of three groups: A, B and C with different options for guarantees of mechanical properties and chemical composition.
Group A steels were designated in the same way as according to the current GOST 380-2005, eg, St3kp. The corresponding letter was added to the steels of groups B and C in front, eg, VSt3kp.
Current GOST 380-2005 (yes, even an earlier GOST 380-94) unlike earlier editions, it determines only the chemical composition of steels. Mechanical and other properties define standards for specific types of rolled steel, eg, GUEST 535-88 for long products and shapes, and GOST 14637-89 - for heavy-plate products.
4 Hot-rolled steel from St3 steel
4.1 Rental categories according to GOST 535-2005
4.1.1 Depending on the standardized indicators of mechanical properties, rolled products are divided into categories from 1 to 7.
4.1.2 Indicators of mechanical properties, which are used to control the mechanical properties of rolled products:
– temporary resistance: All categories;
– yield point: All categories, except category1;
– relative extension: All categories;
– cold bend: All categories, except category 1;
– impact strength KCU at temperature +20 ° C: category 3;
– impact toughness KCU at a temperature of –20 ° С: category 4;
– impact strength KCU after mechanical aging: category 5;
– impact strength KCV at temperature +20 ° C: category 6;
– impact toughness KCV at -20 ° С: category 7.
4.2 Mechanical properties of rolled products according to GOST 535-2005 made of steel St3
4.2.1 Strength properties of rolled steel St3
4.2.2 Impact toughness of rolled steel St3
5 Application of steel St3
Steel St3kp is used mainly for secondary and lightly loaded elements of welded elements and non-welded structures, operating in the temperature range from minus 10 to 40 ° C.
Steel St3ps and St3sp are used in more critical cases, eg, for load-bearing and non-load-bearing elements of welded and non-welded structures and parts, working at positive temperatures.
Shaped and sheet steel with a thickness of up to 36 mm for load-bearing elements of welded structures, operating at variable loads in the range from -40 to + 45 ° C, as well as for load-bearing elements of welded structures, working at temperatures from -40 to +45 ° C.
6 Weldability of steel St3
Steel St3 of all grades is welded without restrictions. Welding methods: manual arc, automatic submerged arc and gas shielded, electroslag, contact point. For thicknesses over 36 mm recommended heating and subsequent heat treatment.
7 Forging modes of steel St3
Forging start temperature - 1300 ° C.
End forging temperature - 750 ° C.
8 Tempering brittleness of steel St3
9 Flockens in St3 steel
Not flock sensitive